Mozilla looks set to miss its February deadline for the release of its forthcoming browser Firefox 4.

The open-source outfit delayed building beta 12 of Firefox 4 late last week, because Mozilla wanted to stamp out the few remaining hardblocker bugs found in the browser, before releasing the latest test build.

Earlier this month, Mozilla seemed pretty confident that the 12th Firefox 4 beta would be the final test iteration, after originally mulling the prospect of a pushing out a 13th beta.

"As of now, beta 12 is the last planned beta," Mozilla's Christian Legnitto wrote last week.

"We reserve the right to have a beta 13 if issues found in beta 12 need additional coverage before a release candidate (RC)."

However, beta 12 has been temporarily iced while the team await the final list of bugs, or "betaN hardblockers[1]", prior to releasing that test build.

All of which could push the final release of Firefox 4 into March. The browser has been subjected to a series of delays, while Mozilla has battled to get its bugs list down to zero.

Mozilla's Asa Dotzler saw reasons to be cheerful this morning.

"From what I can tell, there are only seven unwritten patches standing between Firefox 4 and hundreds of millions of users. yay :-)" he wrote on Twitter. ®